Dyson suggests replacing the filter every year but you could vacuum off the dust on the outside. Their vacuum cleaner filters are washable which is probably where OP got the idea.
Having just gone back to a bagged vacuum, I genuinely wonder why people ever accepted bag-less vacuums in the first place.
Aside from the “empty the canister out and watch all fine dust float back into my house” issue, vacuum bags function as one massive filter. It’s not physically possible to build a filter into a bag less vacuum that approaches the size or capability of the vacuum bag itself.
Bags are a razors + blades model. The vacuum is $100 but the bags are $30 for 3 if you buy the branded bags. Plus the suction on a bagged vacuum measurably decreases before the bag is full.
These days I have a roomba and a Dyson cordless stick vacuum for occasional use.
Then I imagine part of it is the fact that people are willing to spend $x on a fan (of any sort) and $x+y on an air purifier.
If an air purifier is generally accepted to be a higher-price item, then making a fan into one with some sort of filter helps justify the higher price.
(Just speculation, though. I have no info about their design or marketing decisions.)
